—one atom gives up an electron to become a “cation”; the othergets that electron to become an “ion”. These now-charged atoms are attracted byelectrostatic forces. Omnidirectional.

Example: Na (+) (small) and Cl (-)(large)

Packing: as close as possible.

c) Metallic bonds

--hold metals and alloys together. Allows for densepacking of atoms, hence metals are heavy. Outer orbit gives up one electron(on average) which is free to roam Resulting metal ions (+1) are heldtogether by “sea” of electrons. Good electrical conductivity.Omnidirectional.

2. Bonds holding molecules together

a) Hydrogen bonds

--organic compounds often held together by charged-OH (hydroxyl) groups. Directional. Due to distribution of charge onmolecule. Weak.

++-b) Van der Waal forces

--forces arising from surface differences acrossmolecules. Like polar molecules, but not fixed in direction. Very weak.

Example: H2O

Covalent bonding (angle of 104o)

“polar molecule”

Hooke's Law

A. Robert Hooke, 1679 "As the extension, so the force",

i.e., stress is proportional to strain

B. Hooke's law: an approximation of the relationship between thedeformation of molecules and interatomic forces.